Understanding the pH of Soil for a Successful Garden

If you are working against the pH in your soil, all your gardening efforts could be wasted. Your soil pH may determine which plant species thrive and which do not. In order to have the most successful planting experience, you need to know how to measure the pH of your soil, what the results mean to you and how to alter it if necessary.

What pH Stands for
The term pH stands for the potential or percentage of hydrogen ions in a solution. In soil, the hydrogen ions are in the water that fills the pores between soil particles. The more hydrogen ions in a solution, the more acidic it is.

Soil is composed of minerals from dissolved and crushed rocks and of organic matter, air and water. The types of rocks that formed the soil in an area added different minerals to the soil. Some of the minerals are beneficial to plants and some are not. Hydrogen gets into soil from the rocks, from the breakdown of organic matter and from chemical reactions in root systems. Different minerals in the soil dissolve and become available to plants at different levels of pH.

A pH scale is a way to rate how acidic or alkaline soil is. It ranges from 0 to 14. Seven is considered neutral. Above seven is alkaline and below seven is acidic. The pH increases or decreases by 10 times for each point on the scale. A pH of 6 is 10 times more acidic than 7, and a pH of 5 is 10 times that, or 100 times more acidic, than a pH of 7.

What pH Means to Gardeners
How acidic or alkaline the water in soil is determines what kinds of mineral elements are dissolved and become available to plants. Most plants grow best at pH levels of 6.5 to 7.5. That is where the most beneficial minerals become available to them. A few plants have adapted to survive in pH levels slightly higher or lower than that.

In addition, the pH level in soil also affects the microbes and microorganisms that break down organic matter that adds nutrients to soil. They like to grow at about the same pH level that plants do.

The soil your plants are in can have all the essential elements needed for producing food, but if they are unavailable because of a pH that's too high or too low, the plants can't use them and will suffer. Certain plants are more sensitive to the loss of certain minerals, such as iron. When the pH of soil goes above 6.5, iron becomes largely unavailable to plants. Some plants, like Pin Oaks, will quickly decline. In other cases, the pH level may cause toxic elements, such as aluminum, to become too available to plants.

In most areas, a wide range of plants will grow, but your soil pH may determine whether some species will survive in your garden. But even though plants will continue to survive, that doesn't always mean all is well. Marginal deficiencies caused by pH problems may cause your plants to become more susceptible to disease and insect attacks because their immune systems aren't as effective.

Pesticides may not work effectively if your soil pH is too high or low. They are developed for use in the pH range that most plants prefer. The chemicals in them may react with elements available in high- or low-pH conditions.

Finding Your Soil's pH
You can get your soil tested at almost any County Extension office in the United States. Many garden and farm-service stores also offer this service. They will tell you how they want you to collect and submit the specimen. These places will generally give you the soil pH with recommendations for fertilizing to change it, if necessary.

There are small kits available that have you mix water and soil and test the pH, but these are not very reliable. If you are a person who likes to do it yourself, you can purchase a small meter that has probes that go into moist soil and read the pH. The more expensive ones used by professional growers are more accurate.

Changing Your Soil's pH
Soil pH can be raised much more easily than lowered. If your results are only slightly out of optimum range and your plants seem to be growing well, don't worry too much. Adding lots of organic matter and working it into the soil will help balance soil pH. Lime can be added to soil that is too acidic to raise the pH. This works fairly quickly. Don't add lime until you know your soil needs it, and follow the recommendations for your situation. Soil may be acidic if it is too wet from poor drainage or lacking air from soil compaction. Changing these conditions may help.

Lowering soil pH is harder and takes longer than raising it. Too much lime or too many wood ashes can raise soil pH, as can natural conditions. Adding organic matter helps. Fertilizers such as ammonium nitrate or ammonium sulfate will tend to lower pH. These are often marketed as fertilizers for acid-loving plants. If the drainage is good, lots of rainwater or softened water may leech out some of the alkaline elements over time.

For small areas, aluminum sulfate or sulfur can be tried. You will need to consult with your County Extension Service or other garden expert to find out how much to use on your soil. This method will be quite expensive.

Choosing plants that like the soil pH you have in your yard is another good way to minimize plant stress, providing the soil pH is not too high or low. There are plants that like both more acidic and more alkaline conditions.